Preheat oven to 400 F. Grease a GoodCook casserole dish and set aside.
Melt butter in a medium saucepan over medium heat. Add shallots and mince garlic and cook for 1-2 minutes or until fragrant. Whisk in flour to butter mixture and cook until smooth and golden in color, about 1-2 minutes.
Slowly add in the milk and heavy cream whisking as your pour. To cream add in salt, pepper, rosemary and thyme to cream mixture. Cook for 3-4 minutes, the mixture should be thick enough to coat the back of a wooden spoon.
Remove cream mixture from heat and whisk in shredded smoked gouda, and 1 cup of shredded gruyere cheese until smooth.
In the casserole dish, arrange one layer of thinly sliced potatoes, slightly overlapping each other. Spread one third of the melted cheese mixture over potatoes and continue to layer two more potato layers until you’ve reached the top of the casserole dish.
Cover with foil and cook for 30 minutes or until potatoes are tender. Remove foil and sprinkle with remaining ½ cup of gruyere. Return potatoes to oven and cook for an additional 20-25 minutes or until cheese is golden brown and bubbly.